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Reaching activity in parietal area V6A of macaque: eye influence on arm activity or retinocentric coding of reaching movements?

Marzocchi N, Breveglieri R, Galletti C, Fattori P - Eur. J. Neurosci. (2008)

Bottom Line: The present study was aimed to disentangle the gaze effect from the effect of reaching activity upon single V6A neurons.The majority of V6A reaching neurons use a system that encompasses both of these reference frames.These results are in line with the view of a progressive visuomotor transformation in the dorsal visual stream, that changes the frame of reference from the retinocentric one, typically used by the visual system, to the arm-centred one, typically used by the motor system.

View Article: PubMed Central - PubMed

Affiliation: Dipartimento di Fisiologia Umana e Generale, Università di Bologna, I-40126 Bologna, Italy.

ABSTRACT
Parietal area V6A contains neurons modulated by the direction of gaze as well as neurons able to code the direction of arm movement. The present study was aimed to disentangle the gaze effect from the effect of reaching activity upon single V6A neurons. To this purpose, we used a visuomotor task in which the direction of arm movement remained constant while the animal changed the direction of gaze. Gaze direction modulated reach-related activity in about two-thirds of tested neurons. In several cases, modulations were not due to the eye-position signal per se, the apparent eye-position modulation being just an epiphenomenon. The real modulating factor was the location of reaching target with respect to the point gazed by the animal, that is, the retinotopic coordinates towards which the action of reaching occurred. Comparison of neural discharge of the same cell during execution of foveated and non-foveated reaching movements, performed towards the same or different spatial locations, confirmed that in a part of V6A neurons reaching activity is coded retinocentrically. In other neurons, reaching activity is coded spatially, depending on the direction of reaching movement regardless of where the animal was looking at. The majority of V6A reaching neurons use a system that encompasses both of these reference frames. These results are in line with the view of a progressive visuomotor transformation in the dorsal visual stream, that changes the frame of reference from the retinocentric one, typically used by the visual system, to the arm-centred one, typically used by the motor system.

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Gaze modulation on the holding phase of reaching (epoch HOLD): average population behaviour of V6A neurons modulated in HOLD. (A and B) Normalized population responses of V6A neurons showing consistent (A) or inconsistent (B) patterns of modulation in FIX and HOLD epochs. (C) Normalized population responses of V6A neurons modulated by gaze direction in HOLD but not in FIX epochs. Preferred/non-preferred conditions were, respectively, the one with the highest activity in HOLD epoch, and the one with the lowest. The activity of cells in each population was aligned twice (on cue onset and on onset of hold epoch, respectively). Other details as in Fig. 4.
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fig06: Gaze modulation on the holding phase of reaching (epoch HOLD): average population behaviour of V6A neurons modulated in HOLD. (A and B) Normalized population responses of V6A neurons showing consistent (A) or inconsistent (B) patterns of modulation in FIX and HOLD epochs. (C) Normalized population responses of V6A neurons modulated by gaze direction in HOLD but not in FIX epochs. Preferred/non-preferred conditions were, respectively, the one with the highest activity in HOLD epoch, and the one with the lowest. The activity of cells in each population was aligned twice (on cue onset and on onset of hold epoch, respectively). Other details as in Fig. 4.

Mentions: The same population analysis previously described for neurons modulated in the MOV epoch (see Fig. 4) was repeated for neurons modulated in HOLD, as shown in Fig. 6. It is important to note that the subpopulation of neurons included in this analysis was partially different from the one considered in Fig. 4. For example, the neuron in Fig. 5, which was modulated during HOLD but not during MOV, was included only in the analysis of Fig. 6. Neurons modulated in HOLD were divided in three groups shown in Fig. 6, based on the relationships between gaze and HOLD modulations (see Materials and methods, post hoc tests). For each neuron we took into account the response in the preferred condition (condition with the highest activity in HOLD epoch) and in the non-preferred condition (worst response in HOLD). Continuous lines represent the preferred condition, and the dashed lines the non-preferred one. Population responses for neurons modulated in HOLD presented similar features to the ones observed for neurons modulated in MOV (compare Fig. 6 with Fig. 4). Preferred and non-preferred responses in HOLD were well discriminated in all three groups of neurons, indicating a good range of modulation in all types of cell. For neurons showing patterns of modulation of gaze and action epoch, which were consistent one to another (Fig. 6A), the separation between the two curves started with the beginning of fixation, as expected, and was maintained all throughout the duration of the task, suggesting that for these neurons the modulation was mainly driven by the gaze signal.


Reaching activity in parietal area V6A of macaque: eye influence on arm activity or retinocentric coding of reaching movements?

Marzocchi N, Breveglieri R, Galletti C, Fattori P - Eur. J. Neurosci. (2008)

Gaze modulation on the holding phase of reaching (epoch HOLD): average population behaviour of V6A neurons modulated in HOLD. (A and B) Normalized population responses of V6A neurons showing consistent (A) or inconsistent (B) patterns of modulation in FIX and HOLD epochs. (C) Normalized population responses of V6A neurons modulated by gaze direction in HOLD but not in FIX epochs. Preferred/non-preferred conditions were, respectively, the one with the highest activity in HOLD epoch, and the one with the lowest. The activity of cells in each population was aligned twice (on cue onset and on onset of hold epoch, respectively). Other details as in Fig. 4.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2268963&req=5

fig06: Gaze modulation on the holding phase of reaching (epoch HOLD): average population behaviour of V6A neurons modulated in HOLD. (A and B) Normalized population responses of V6A neurons showing consistent (A) or inconsistent (B) patterns of modulation in FIX and HOLD epochs. (C) Normalized population responses of V6A neurons modulated by gaze direction in HOLD but not in FIX epochs. Preferred/non-preferred conditions were, respectively, the one with the highest activity in HOLD epoch, and the one with the lowest. The activity of cells in each population was aligned twice (on cue onset and on onset of hold epoch, respectively). Other details as in Fig. 4.
Mentions: The same population analysis previously described for neurons modulated in the MOV epoch (see Fig. 4) was repeated for neurons modulated in HOLD, as shown in Fig. 6. It is important to note that the subpopulation of neurons included in this analysis was partially different from the one considered in Fig. 4. For example, the neuron in Fig. 5, which was modulated during HOLD but not during MOV, was included only in the analysis of Fig. 6. Neurons modulated in HOLD were divided in three groups shown in Fig. 6, based on the relationships between gaze and HOLD modulations (see Materials and methods, post hoc tests). For each neuron we took into account the response in the preferred condition (condition with the highest activity in HOLD epoch) and in the non-preferred condition (worst response in HOLD). Continuous lines represent the preferred condition, and the dashed lines the non-preferred one. Population responses for neurons modulated in HOLD presented similar features to the ones observed for neurons modulated in MOV (compare Fig. 6 with Fig. 4). Preferred and non-preferred responses in HOLD were well discriminated in all three groups of neurons, indicating a good range of modulation in all types of cell. For neurons showing patterns of modulation of gaze and action epoch, which were consistent one to another (Fig. 6A), the separation between the two curves started with the beginning of fixation, as expected, and was maintained all throughout the duration of the task, suggesting that for these neurons the modulation was mainly driven by the gaze signal.

Bottom Line: The present study was aimed to disentangle the gaze effect from the effect of reaching activity upon single V6A neurons.The majority of V6A reaching neurons use a system that encompasses both of these reference frames.These results are in line with the view of a progressive visuomotor transformation in the dorsal visual stream, that changes the frame of reference from the retinocentric one, typically used by the visual system, to the arm-centred one, typically used by the motor system.

View Article: PubMed Central - PubMed

Affiliation: Dipartimento di Fisiologia Umana e Generale, Università di Bologna, I-40126 Bologna, Italy.

ABSTRACT
Parietal area V6A contains neurons modulated by the direction of gaze as well as neurons able to code the direction of arm movement. The present study was aimed to disentangle the gaze effect from the effect of reaching activity upon single V6A neurons. To this purpose, we used a visuomotor task in which the direction of arm movement remained constant while the animal changed the direction of gaze. Gaze direction modulated reach-related activity in about two-thirds of tested neurons. In several cases, modulations were not due to the eye-position signal per se, the apparent eye-position modulation being just an epiphenomenon. The real modulating factor was the location of reaching target with respect to the point gazed by the animal, that is, the retinotopic coordinates towards which the action of reaching occurred. Comparison of neural discharge of the same cell during execution of foveated and non-foveated reaching movements, performed towards the same or different spatial locations, confirmed that in a part of V6A neurons reaching activity is coded retinocentrically. In other neurons, reaching activity is coded spatially, depending on the direction of reaching movement regardless of where the animal was looking at. The majority of V6A reaching neurons use a system that encompasses both of these reference frames. These results are in line with the view of a progressive visuomotor transformation in the dorsal visual stream, that changes the frame of reference from the retinocentric one, typically used by the visual system, to the arm-centred one, typically used by the motor system.

Show MeSH
Related in: MedlinePlus